1. Field of the Invention
The present invention relates to large scale data processing systems which include multiple CPUs and main storage units, and more particularly to the problem of preserving the availability and contents of the main storage units when the system is partitioned for maintenance activities.
2. Description of Related Art
Current computing complexes which can be partitioned are built with a plurality of "sides", each side physically containing a set of computing resources, such as CPUs, I/O processors, main storage units, cache memory systems, and other facilities interconnected through a system controller for the side. When joined, the system controllers on the plural sides communicate with each other to allow access to all of the physical main storage units as a single logical storage array from any processor in the complex. The connection between the system controllers can be broken and the systems partitioned into two independent systems to allow maintenance activity to be performed on one side of the complex, while the other side continues to operate. In current art, the main storage units of the system are also involved in the partitioning, such that the memory on the side of the complex affected by maintenance activity is unavailable to the surviving side.
The partitioning of the main storage units has two detrimental effects. First, the main storage units which will be partitioned away from the system must be taken offline to the operating system. Depending on what applications are running, this can be a very time consuming process. Second, the loss of memory creates an additional performance loss to the surviving system on top of the loss of processor power.
Accordingly, it is desirable to provide a system in which all of the memory can be kept available to the operating system, even after the system has been partitioned into two physical systems in order to isolate units of the system for maintenance.